1. Field of the Invention
This invention is directed to an improved fuel injector, having a pressure booster, for injecting fuel into an internal combustion engine.
2. Description of the Prior Art
Stroke-controlled fuel injection systems with a high-pressure collection chamber (common rail) are increasingly used for introducing fuel into the combustion chambers of direct-injection internal combustion engines. The advantage of this is that the injection pressure of the fuel into the combustion chambers can be adapted to the engine load and engine speed. For reducing emissions and to attain high specific power levels, a high injection pressure is required. Since the attainable pressure level in high-pressure fuel pumps is limited for reasons of strength, to further increase the pressure in fuel injection systems with a high-pressure collection chamber (common rail), a pressure booster can be used in the fuel injector.
German Patent Disclosure DE 101 23 913 relates to a fuel injection system for internal combustion engines that has a fuel injector which can be supplied from a high-pressure fuel source. A pressure booster device that has a movable pressure booster piston is connected between the fuel injector and the high-pressure source. The pressure booster piston divides a chamber, which can be connected to the high-pressure source, from a high-pressure chamber that can be made to communicate with the fuel injector. By filling a return chamber of the pressure booster with fuel, or evacuating fuel from the return chamber, the fuel pressure in the high-pressure chamber can be varied. The fuel injector has a movable closing piston for opening and closing injection openings. The closing piston protrudes into a closing pressure chamber, so that the closing piston can be acted upon by fuel pressure, to attain a force acting on the closing piston in the closing direction. The closing pressure chamber and the return chamber are formed by a common closing-pressure return chamber, in which all the portions of the chamber communicate permanently with one another for exchanging fuel. A pressure chamber is provided for supplying injection openings with fuel and for acting upon the closing piston with a force acting in the opening direction. A high-pressure chamber communicates with the high-pressure fuel source in such a way that in the high-pressure chamber, aside from pressure fluctuations, at least the fuel pressure of the high-pressure fuel source can be constantly applied. The pressure chamber and the high-pressure chamber are formed by a common injection chamber, and all the portions of the injection chamber communicate permanently with one another for exchanging fuel.
German Patent Disclosure DE 102 47 903.8 relates to a pressure-boosted fuel injection device with a control line embodied on the inside. The fuel injection device communicates with a high-pressure source and includes a multi-part injector body. Received in the injector body is a pressure booster, which can be actuated via a differential pressure chamber and whose pressure booster piston divides a work chamber from the differential pressure chamber. The fuel injection device can be actuated via a switching valve. A pressure change in the differential pressure chamber of the pressure booster is effected via a central control line that extends through the pressure booster piston. The switching valve can be embodied as either a magnet valve or a servohydraulic 3/2-way valve.